J. Anim. Sci. 2005. 83:243-254
© 2005 American Society of Animal Science
Diet modifications to improve finishing pig growth performance and pork quality attributes during periods of heat stress1,2
J. D. Spencer*,3,
A. M. Gaines*,
E. P. Berg* and
G. L. Allee*,4
* Department of Animal Sciences, University of Missouri, Columbia 65211
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Abstract
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A total of 196 barrows (88 kg) were used in a 2 x 2 factorial arrangement of treatments and housed in a facility (seven pigs per pen) where temperatures cycled between 27 and 35°C. Treatments consisted of (as-fed basis) two CP levels (13.6 or 11.3%) and two levels of added fat (1 or 8%). Diets were formulated to the same true digestible lysine:ME ratio (1.68 g of lysine/Mcal of ME). Diets were fed and growth variables were measured until pigs reached 114 kg of BW. Ham and LM (loin) 24-h pH (PH24), and light reflectance (CIE L*, and a*, and b*, and hue angle) were taken after slaughter. Additionally, loins were removed and measured for i.m. fat, moisture, glycolytic potential, and subjected to a 7-d retail display evaluation that measured pH, light reflectance, and subjective color and odor score. The remaining boneless lumbar loin segment was vacuum-sealed for 14 d and subsequently measured for pH, light reflectance, and color. Pigs fed the high-CP, low-fat diet had a lower ADG than all other treatments (P = 0.06). High-fat feeding resulted in improved ADG (CP x Fat; P = 0.06) and G:F (Fat effect; P < 0.01). Higher fat and lower protein levels both increased final BF (P = 0.07). Pigs fed the low-CP diets had lower ham PH24 (P < 0.01). Loin PH24 was higher with high fat feeding (P = 0.10). Additionally, pigs fed high fat diets had lower L* values on the ham face and cut loin 24 h after slaughter (Fat effect; P 
0.02). These loin color differences were maintained through the 7-d retail display and 14-d storage period. There were no differences in loin i.m. fat or moisture content; however, high-fat feeding tended to decrease loin glycolytic potential (P = 0.11). These results suggest that in a hot environment, decreased CP content improved finishing pig ADG when dietary fat supplementation was low. High dietary fat inclusion during heat stress improved ADG and G:F, especially when CP level was elevated. High-fat diets fed in a hot environment increased pork color intensity by decreasing the glycolytic potential at slaughter and elevating muscle pH.
Key Words: Heat Stress • Pigs • Pork Quality
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Introduction
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Finishing pigs are particularly susceptible to high temperatures due to their decreased evaporative critical temperature (Black et al., 1999
) and the stocking density during this phase of production. In previous reports, the digestion of dietary protein increased animal heat production (Forbes and Swift, 1944; Le Bellego et al., 2001), whereas digestion of fat dramatically lowered the thermal effect of feeding (Forbes and Swift, 1944). Both methods of reducing the dietary heat increment have been shown to improve pig growth performance during high temperatures independently (Stahly et al., 1979; Stahly and Cromwell, 1979), or in combination (Spencer et al., 1999, 2000). However, the benefits of reducing CP intake at multiple levels of dietary fat have not been reported.
Long-term stressors (Briskey et al., 1959, 1960; Witte et al., 2000) and decreased dietary carbohydrate content (Briskey et al., 1959, 1960; Rosenvold et al., 2001) decrease the glycogen content of muscle at the time of slaughter, and increase the color intensity of pork. In addition to improving energy intake and growth performance, especially in hot environments, increased fat supplementation may reduce the glycolytic potential of pork as saturated fat intake has been shown to decrease both insulin sensitivity and responsiveness in skeletal muscle (Grundleger and Thenen, 1982; Sha et al., 1995). High levels of fat inclusion in late-finishing swine diets may provide an additional opportunity to decrease the amount of glycogen present in the muscle at the time of slaughter and reduce the incidence of pale lean color postmortem.
The objectives of this experiment were to determine the effects of decreasing the dietary CP content with two levels of fat supplementation for late-finishing swine housed in a cycling hot environment. The effects of these nutritional modifications on muscle glucose storage and pork quality development were also evaluated.
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Materials and Methods
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One hundred ninety-six late-finishing barrows (Dalland x PIC C-22, 77 kg of BW) were selected from a commercial farm (Princeton, MO) and transported to an off-site finishing facility. Pigs were blocked by weight and assigned to one of four dietary treatments in a 2 x 2 factorial arrangement of treatments consisting of (as-fed basis) two levels of fat addition (1 or 8% added fat) and two levels of dietary CP (11.3 or 13.6%). All diets were formulated to contain 1.68 g of true ileal digestible lysine/Mcal of ME (Table 1). Diets were steam-pelleted with a 4.45-cm-thick die to make a 4.8-mm pellet and were stored in 22.7-kg paper bags. The University of Missouri Animal Care and Use Committee approved all procedures.
Housing
Pigs were housed in a naturally ventilated facility with supplemental heat so that the environmental temperature within the barn cycled between 27°C (1900 to 1000) and 35°C (1000 to 1900) starting at the initiation of the experiment. The trial was conducted from June through August. Temperature and relative humidity were continuously measured inside the research facility for the entire experimental period (H8 Pro Series, Onset Computer Corp., Pocasset, MA) (Figure 1). The supplemental heat provided the desired cycling heat stress environment (temperature 32.05 ± SD 2.05°C; relative humidity 62.02 ± SD 11.76%); however, relative humidity fluctuated with the natural environment. Seven pigs were placed in each pen (3.15 x 1.75 m). Pens allowed for 0.79 m2 of space per pig. The floors in all pens consisted of total concrete slats. All pigs had ad libitum access to one two-hole feeder and nipple waterer. There were seven replicate pens per treatment.
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Figure 1. Temperature (°C) and relative humidity inside the experimental naturally ventilated finishing facility (temperature 32.05 ± 2.05°C; relative humidity 62.02 ± 11.76%). Temperature was adjusted by setting the thermostat to 27°C (1900 to 1000) and 35°C (1000 to 1900). Relative humidity fluctuated with the natural environment.
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Measurements
Pigs were fed a corn and soybean meal diet that met all nutrient requirements (NRC, 1998) and contained (as-fed basis) 4% supplemental choice white grease, 14.7% CP, 0.70% true ileal digestible lysine, and 3.38 Mcal of ME/kg during an acclimation period that allowed pigs to adjust to pens and pen mates for 14 d before the initiation of the study (approximately 88 kg of BW). On d 1 of the study, pigs were measured for 10th-rib backfat (BF) and LM area (LMA) by real-time ultrasound (model SSD-500 V, Aloka Co. Ltd., Tokyo Japan), and fed their assigned dietary treatment. Feed intakes and BW gains were recorded weekly until the block average was approximately 114 kg of BW.
Carcass Evaluation
All animals were subjected to ultrasound to measure final BF and LMA before being transported 88 km to a commercial processor. Feed access was removed 2 h before transportation. Pigs were unloaded at the processor and placed in pens for approximately 3 h before slaughter. In liarage pens, water was sprayed over all pigs. Electrical stunning (320 V for 2 s) was head to back. All pigs were transported to the stunner on an elevated restraining conveyor. Immediately after slaughter, measurements of carcass weight, 10th-rib fat depth (FOM BF), and LM depth (FOM LMD) were determined with an optical probe (Fat-O-Meater; SFK Technology, Peosta, IA). Percentage of carcass lean (FOM Lean) was calculated using a proprietary company derived formula and recorded for each carcass. Carcasses were then placed within a cooler (3°C) and further chilled via a conventional spray chill system. At 22 h postmortem, carcasses were removed from the cooler to undergo commercial fabrication. The right ham from all carcasses was evaluated by an online primal cut electromagnetic scanner (AgMed Inc., Springfield, IL) to determine ham weight and the total body electrical conductivity of the cut ham to estimate lean ham content. After total body electrical conductivity analysis, all hams were subjected to intramuscular pH (pH star-probe, SFK Technology, Peosta, IA) measurements in the semimembranosus muscle 24 h after slaughter. Light reflectance (CIE L*, a*, b* values; HunterLab MiniScan XE Plus, Reston, VA), using a light source of D65/10° standardized to a black and white tile, and calculated hue angle (Arc tangent [b*/a*] x [360°/{2 x 3.14}]; Liu et al., 1996) were collected on the cut lean surface of the gluteus medius muscle approximately 24 h postmortem.
The whole LM from the right side of the carcass was collected from three to four carcasses per pen representing the average pen carcass weight, vacuum-sealed, and transported to the University of Missouri for fabrication and quality evaluation. One boneless chop (2.54 cm) was removed from the lumbar section of each LM at the 10th rib, blotted dry, weighed, and placed in a Styrofoam tray covered with oxygen-permeable plastic film, and stored for 7 d under constant lighting at 3°C in a simulated retail display. Muscle weight, light reflectance (L*, a*, b*), calculated hue angle, and i.m. pH were evaluated on d 0, 1, 3, 5, and 7 of retail display storage. Additionally, subjective color and odor scores were obtained on d 0, 1, 3, 5, and 7 of storage. Subjective color score ranged from 1 (bright grayish pink) to 5 (dark pinkish red). Subjective odor score of samples under retail display simulation were evaluated using a five-point scale with scores of 1 and 5 representing samples with no oxidation odor (typical fresh pork odor) and extreme oxidation odor, respectively. A second, 2.54-cm boneless chop was removed from the LM (approximately the 11th rib) for determination of Warner-Bratzler (WB) shear force. For WB shear determination, chops were placed on a Farberware open hearth grill (model 455N, Walter Kidde, Bronx, NY), cooked to 35°C, turned, and cooked to a final temperature of 70°C. Temperature was monitored using a 12-channel scanning thermocouple thermometer (Cole-Parmer Instrument Co., Vernon Hills, IL). Samples were allowed to cool to room temperature (18°C). Six core samples (1.27-cm diameter) were excised from each LM parallel to the muscle fiber, and sheared perpendicular to the fiber orientation. The remaining portion of the fresh LM lumbar section was weighed, vacuum sealed, and stored at 2°C for 14 d to simulate domestic storage. Muscle weight, i.m. pH, light reflectance (L*,a*,b*), calculated hue angle, cooking loss, and WB shear force were determined on removal from 14 d of storage.
One additional chop was removed from the LM at the ninth rib, trimmed of all external fat and connective tissue, and stored (–80°C) for later determination of percentage of moisture, fat content, and glycolytic potential (GP). Methods for analyzing GP were conducted by modifying the methods reported by Monin and Sellier (1985) and Lonergan et al. (2001). The procedure consisted of extracting cores from the LM totaling 2 g and placing them in 10 mL of ice-cold perchloric acid (0.6 N). Then, 1 mL of amyloglucosidase (Sigma Chemical Co., St. Louis, MO) was added to each tube for glycogen hydrolysis followed by the addition of 20 µL of 5.4 N KOH. Samples were vortexed, and then incubated for 120 min at 37°C. Samples were then cooled for 10 min before adding 100 µL of ice cold 3 N perchloric acid and clarifying samples by centrifuging (7,000 x g, 4°C) for 5 min. Micromolar glucosyl units (glucose, glucose-6-P, and molecular glycogen) were determined in duplicate using a glucose (HK) assay kit (Sigma Chemical Co.), with absorbency quantified at 520 nm (Beckman DU-65 spectrophotometer, Beckman Instruments, Inc., Fullerton, CA). For lactate determination, duplicate homogenate samples (100 µL) were mixed with reagents from a kit with premixed reagents (Sigma Chemical Co.). Samples were incubated for 15 min at 37°C. Lactate concentration was determined at a wavelength of 340 nm (Beckman DU-65 spectrophotometer). Glycolytic potential was calculated using the following equation described by Monin and Sellier (1985) and Lonergan et al. (2001): 2[(glycogen) + (glucose) + (glucose-6-phosphate)] + (lactate).
Statistics
Growth performance, carcass measurements, and simulated domestic storage data were analyzed as a randomized complete block design with a 2 x 2 factorial arrangement of treatments consisting of two levels of fat addition (1 or 8%) and two levels of dietary CP (11.3 and 13.6%). The pen of pigs was used as the experimental unit. Carcass measurements for FOM BF, FOM LMD, ham lean, ham weight, and dressing percent were adjusted by covariate analysis for hot carcass weight. Final BF and LMA were adjusted for the covariant of initial BF and LMA, respectively. Analysis was performed using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC) and tested for the main effects and all possible interactions. Means were separated using Fisher’s Protected LSD test.
Retail display simulation was analyzed as a split-plot in time as outlined by Gill and Hafs (1971). The variance/covariance matrix over time was tested for structure, which indicated compound symmetry. The linear statistical model included level of fat addition, level of dietary CP, day of analysis, pig within fat x CP interaction, and all possible interactions. When interactions of the main effects were found, treatment means were separated using the protected LSD test. Split-plot in time procedures were conducted using the Proc Mixed procedure of SAS.
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Results
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Growth Performance and Ultrasound Measurements
Pigs consuming the diet with low CP (11.3%) and a low level of fat addition had a higher rate of feed intake than all other treatments (P < 0.01; Table 2). Pigs fed diets with higher CP displayed similar levels of feed intake regardless of the level of fat addition. At the 8% added fat level, pigs consuming diets with lower CP had a lower feed intake than those fed diets with 13.6% CP (P < 0.05). Pigs consuming diets with a high level of fat supplementation had a greater ADG, especially if the CP level was higher (CP x fat; P = 0.06). Pigs consuming a diet with 1% fat addition and a decreased level of CP, or a diet with 8% added fat grew faster in the hot environment (P = 0.06). However, due to the elevated feed intake by pigs fed the low CP and low fat diet, only the addition of 8% fat improved feed efficiency (fat effect; P < 0.01). Pigs fed diets with a decreased CP level at both levels of fat addition had greater amounts of final BF (P = 0.03), and there was a trend for reduced LMA (P = 0.12) as determined by ultrasound before slaughter (Table 2).
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Table 2. Growth performance and ultrasound measurements at the 10th rib of barrows reared in a cycling hot environment and fed different levels of crude protein and fata,b
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Carcass Measurements
There were no effects of CP level or fat addition on processing plant measurements of FOM LMD, FOM Lean, or carcass dressing percent (Table 3). High fat addition increased carcass weight and FOM BF (Fat effect; P 0.05) and decreased ham lean percent (P = 0.08; Table 3). Feeding a lower CP diet decreased the ham weight, ham lean weight, and percent ham weight of the carcass, independent of the level of fat addition (CP effect; P 0.04; Table 3).
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Table 3. Carcass characteristics of barrows reared in a cycling hot environment and fed different levels of crude protein and fata,b
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Ham and Longissimus Muscle pH and Light Reflectance
There were no effects of CP level or fat addition on 24-h a* or 24-h b* in the ham or LM (Table 4). Pigs fed diets with a higher level of CP had carcasses with higher 24-h ham pH in the semimembranosus muscle (P < 0.01). However in the LM, 24-h pH was higher (P = 0.10) in pigs fed high-fat diets. Higher fat addition provided darker cut ham and LM lean surfaces as displayed by lower 24-h L* and 24-h hue angle (fat effect; P 0.02 and P 0.08, respectively).
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Table 4. Ham and longissimus muscle characteristic 24 h postmortem from barrows reared in a cycling hot environment and fed different levels of crude protein and fata,b
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Retail Display Simulation and Warner-Bratzler Shear
Cumulative weight loss of the boneless-chop increased throughout the simulated retail display (Day effect; P < 0.01; Figure 2). Longissimus muscles from pigs fed diets with the higher level of CP had higher rates of weight loss throughout the simulation than pigs fed diets with the lower CP level regardless of fat addition (P < 0.01). Longissimus muscle pH decreased to d 3 of retail display and then increased to d 7. There was no effect of CP or fat addition level on LM pH (Figure 3). The duration of retail display influenced LM color. Longissimus muscle L* values increased to d 3 of display and then remained at a static level through d 7 (Figure 4). Pigs fed diets with the higher level of fat had chops that displayed a darker lean surface throughout the retail evaluation. Measurements of CIE L* (Figure 4) and color score (Figure 5) were darker than those from pigs fed a diet with 1% added fat (Fat effect; P < 0.01 and P < 0.05, respectively). Longissimus muscle CIE a* and b* values reached a peak level on d 3, and then decreased on d 5 and d 7. Longissimus muscle hue angle rapidly declined after d 0 for all treatments (P < 0.01). However, by d 3, hue angles remained relatively unchanged until d 7 (Figure 6). There were no effects of CP or fat addition on cooking weight loss or WB shear force (P 
0.11) (Table 5).
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Table 5. Cooking weight loss and Warner-Bratzler shear force of longissimus muscle chops cooked to 70°C from barrows reared in a cycling hot environment and fed different levels of crude protein and fata,b
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Storage (14-d)
Longissimus muscles from pigs fed high-fat diets maintained a darker lean surface through a 14-d vacuum storage than those from pigs fed lower-fat diets, as indicated by lower CIE L* (fat effect; P < 0.01) (Table 6). There were no effects of CP or fat level on LM pH, a*, b*, hue angle, or weight loss after the 14-d period (P 0.11). Treatments did not affect cooking weight loss (P 0.79) or WB shear force (P 0.75).
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Table 6. Quality attributes of vacuum sealed longissimus muscles after storage for 14 d at 2°C from barrows reared in a cycling hot environment and fed different levels of crude protein and fata,b
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Chemical Analyses and Glycolytic Potential
Dietary treatment did not affect LM fat or moisture content (Table 7). Pigs fed diets with 8% added fat had lower levels of glucosyl units in the LM than pigs fed the low fat diets (P = 0.04). Consequently, the lower levels of stored glucose resulted in a trend toward lower glycolytic potential in the LM of pigs fed the high level of fat (P = 0.11; Table 7).
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Table 7. Chemical analysis of longissimus muscle from barrows reared in a cycling hot environment and fed different levels of crude protein and fata,b
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Discussion
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The hot environment severely reduced late-finishing growth performance, but dietary modifications ameliorated these negative affects on BW gain. When the dietary CP level was decreased or fat level was increased in the diet, growth rate improved approximately 7.4 or 11%, respectively, compared with gains of pigs fed the high-CP, low-fat diet. Although reducing excess dietary CP improved growth rate, only fat addition improved feed efficiency. Stahly et al. (1979) also reported improvements in performance and increased carcass fatness with reduced CP diets in a hot environment. Fat addition to swine diets during high temperatures has also been reported to improve growth rate and feed efficiency (Stahly and Cromwell, 1979). However, Le Bellego et al. (2002) found no differences in growth rate or feed efficiency with decreased levels of protein or increased fat supplementation during the late finishing phase of heat-stressed pigs. Using the chemical analysis of the experimental diets (Table 1
), it is possible to more accurately estimate the ME (Noblet and Perez, 1993) and NE (Noblet et al., 1994) content of the experimental diets, and to calculate (DM basis) ME and NE intakes. Decreasing the CP level in the high fat diets reduced ME intake and NE intake by 4.8 and 4%, respectively, compared with pigs fed the high-CP, 8% added-fat diet. However, when the diet contained 1% added fat, decreasing the CP content increased ME and NE intakes by 6.2 and 7.5%, respectively. Improving the daily energy intake of pigs by decreasing the CP content of the lower-energy diets led to a direct improvement in BW gain. Therefore, it seems that when pigs are offered a high-fat diet (8% added fat) ad libitum in a hot environment, there is no further benefit on growth performance of reducing the CP content of the diet. When the dietary fat addition level is low (1%), decreasing the CP level in a hot environment can improve ADG. The results of this study support those of Stahly et al. (1979) and Le Bellego et al. (2001) in that it seems that when energy intake is limiting growth in hot environments, the decreased heat production from lower-protein diets results in more energy available for fat synthesis. Improving ADG by increasing energy intake with fat addition or reduced CP level came predominately as fat accretion, as evidenced by a higher final BF with 8% fat addition and decreased CP level. This response is in agreement with the results of Le Bellego et al. (2002). Alterations in lean tissue accretion and carcass conformation were further influenced by dietary manipulation in the hot environment. Pigs fed the reduced CP diets had decreased ham weights regardless of the level of fat addition. These results were unexpected as the decrease in CP was accomplished without reducing the essential AA and exceeded NRC (1998) requirements. The effects of dietary modifications or reduced dietary CP content on the percentage of carcass proximal components are compelling and require further research.
Pigs fed high-fat diets had heavier carcass weights at the time of commercial processing. The heavier carcass weights from high-fat feeding translated into improvements in packer payment per pig (data not shown). Improvements in the carcass value of pigs fed high-fat diets in a commercial environment were previously reported (Spencer et al., 2000), and were due to a reduction in carcass weight variation and increased carcass weight. Any alterations in pork quality due to environmental conditions or dietary regimen could also alter carcass value.
Pigs fed high-fat diets in the hot environment consistently displayed carcasses with a darker lean surface than pigs fed low-fat diets. The cut lean surface of the ham gluteus medius and longissimus dorsi muscle displayed lower 24 h CIE L* and calculated hue angle after slaughter. Boneless LM chops from pigs fed high fat diets continued to display a darker lean surface throughout a 7-d retail display. These darker characteristics were significant by both objective (CIE L*) and subjective (visual color score) measurements. Furthermore, boneless LM segments continued to display a darker cut lean surface after being vacuum-sealed for 14 d. A pale lean surface of fresh pork is primarily caused by increased postmortem glycolysis, which results in a lower muscle pH (Bowker et al., 2000). The glycogen content of the muscle at the time of slaughter is an important factor influencing ultimate pH (Rosenvold et al., 2001). Pigs fed the lower-fat diets in the hot environment had a higher GP and lower 24-h LM pH than did pigs fed the 8% supplemental fat diet. This finding suggests that feeding high amounts of fat before slaughter in the hot environment decreased the glycogen content of the muscle, which resulted in decreased postmortem glycolysis, reduced pH decline, and a darker lean surface. In previous studies, feeding pigs a low-carbohydrate diet before slaughter decreased ham glycogen content, resulting in a higher postmortem pH and a darker, firmer lean surface (Briskey et al., 1959; 1960). Similar results have been reported in the LM (Rosenvold et al., 2001). Although it is possible that the supplementation of 8% fat reduced the dietary starch content enough (5.5%) to decrease the GP, it is possible that the high rate of fat inclusion in the hot environment before slaughter may have decreased glucose storage in the muscle by other mechanisms. Previous studies have reported that elevated plasma fatty acids inhibit glycogen synthesis by interfering with glucose transport and phosphorylation, and by inhibiting glycogen synthase (Jequier, 1998). High dietary fat supplementation may have altered glucose metabolism by decreasing the translocation or expression of glucose transporter-4 (Clarke, 2000), thereby reducing LM glucose uptake and GP. Previous studies in other species have shown a decrease in both insulin sensitivity and responsiveness in skeletal muscle (Grundleger and Thenen, 1982; Sha et al., 1995) in response to high intakes of saturated fat.
Elevated growing-finishing temperatures have also been shown to decrease L* values (Witte et al., 2000) and GP (Lefaucheur et al., 1991), and to alter biochemical and histochemical characteristics of LM (Lefaucheur et al., 1991). Concentrations of NEFA, triglycerides, and very-low-density lipoproteins have also been reported to be elevated in pigs reared in high ambient temperatures in an attempt to decrease back-fat thickness and reduce thermal insulation (Kouba et al., 2001). It is possible that environmental temperature may affect how nutritional modifications alter postmortem glycolytic activity and pork quality development. Further research is necessary to confirm these possibilities.
Pigs fed diets with decreased CP content yielded chops from the LM with a lower rate of weight loss during retail display evaluation. These results were unexpected because a decreased CP level did not exert any effect on pH, color, or shear force of the LM.
Previous reports have shown increases in pork tenderness through 14 d of storage (van Laack et al., 2001), but data on the effects of dietary treatment on tenderization development are limited. Regardless of dietary treatment, 14-d storage of vacuum-sealed LM segments decreased WB shear force values (approximately 0.60 kg), indicating no dietary interaction with postmortem tenderization. These results further show the efficacy of long-term storage to enhance tenderization development, and that dietary fat or CP level had no influence on its development.
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Implications
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Swine producers can ameliorate the negative effects of heat stress on late-finishing growth rate by decreasing the dietary crude protein level with supplemental amino acids, or by supplementing diets with high levels of fat. Decreasing the crude protein content when the diet already contains a high level of fat does not provide any further benefit. Additionally, producers can influence the color development of pork after slaughter by feeding high levels of fat during periods of heat stress. The mechanism by which fat supplementation exerts these effects is unknown. Environmental temperature before slaughter may influence the mechanism by which dietary fat level decreases glycolytic potential and darkens the color of pork after slaughter.
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Footnotes
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1 Appreciation is expressed to G. Yi, C. Stahl, K. Maddock, G. Rentfrow, and M. Linville for assistance in carcass data collection. 
2 Partial support for this study was provided by Premium Standard Farms, Princeton, MO, and Ajinomoto-Heartland Lysine LLC, Chicago, IL.
3 Current address: United Feeds, P.O. Box 108, Sheridan, IN 46069.
4 Correspondence: Lab 111 Animal Science Research Center (phone: 573-882-7726; fax: 573-884-6093; e-mail: AlleeG{at}missouri.edu).
Received for publication February 21, 2004.
Accepted for publication August 20, 2004.
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Abstract
Introduction
, 11.3%;
, 13.6%). Values represent least squares means of seven replicate pens per treatment with three to four carcasses measured per pen.
